Owing to that, the cement and casing stress states during the wellbore lifespan are also difficult to predict.
Distinguishing between the various hypotheses for sex differences in lifespan has proven difficult, since comparative and experimental approaches often have given results compatible with several explanatory models [ 4- 6, 14, 26].
The trouble with whales, as geneticists see it, is that they have small populations and long lifespans that make it difficult to build a family tree.
However, it would be difficult to undertake lifespan experiments in mice as the light would not penetrate the entire body as it does in flies and hence its influence would not be systemic.
Given the challenges of tracking effects over multiple human lifespans, the evidence is more difficult to interpret, particularly with respect to potential mechanisms, says Tessa Roseboom, a professor of early development and health at the Academic Medical Center in Amsterdam, the Netherlands.
However, mev-1 mutants express only half as much SOD as wild-type and are hypersensitive to paraquat [ 160], which makes it difficult to clearly interpret lifespan results from this strain.
However, given that both TL and these factors are changing and having an effect over the entire lifespan of an individual, it is difficult to establish directionality of effect, particularly when the various factors are so highly correlated.
To complicate matters, the aphid's life-cycle proved difficult to study, as its lifespan differed from Europe to America.
These processes have previously been correlated to chronological aging by others [ 12, 53- 67], but interpreting the dynamics of biological functions throughout the lifespan in multiple tissues has been proved difficult so far.
These cells serve as models for cells that are either difficult to cultivate or have a limited lifespan in vitro.
